Different meanings and different usages.
1. Different meanings. A dog relies on human power, a fox pretends to be a tiger, and it is a metaphor for using power to bully others. A true hero refers to a person who is truly upright and will not bully others.
2. There is a difference between "dog fighting for human power and "fox pretending to be a tiger": "dog fighting for people's power" has a strong derogatory tone and is mostly used in spoken language, while "fox pretending to be a tiger is powerful" comes from ancient books and is more elegant; it is mostly used in written language, and true heroes are mostly used for praise.